1. Field of the Invention
This invention relates generally to waterbeds, and more particularly to systems for reducing undesirable wave motion within waterbed mattresses in response to movement of individuals sitting or lying on such mattresses.
This invention also relates generally to fiber products and to methods for their manufacture, and more particularly to a bonded buoyant fiber product useful in waterbed mattresses and to a method for its manufacture.
2. Prior Art
(a) Waterbed antiwave systems--Some systems for reducing wave motion within waterbed mattresses use a baffle or baffles hung from a buoyant structure or structures. In some cases the baffle is contoured in various ways, and in particular when the baffle is contoured to form a closed or nearly closed structure it has been called a "hydraulic chamber". Hydraulic chambers have been supported by buoyant structures of various kinds, including buoyant pads, sheets or blocks of polyethylene foam. In all hanging-baffle systems, wave energy is expended (against internal friction of the water) in moving the baffle--and, more importantly, in moving as a unit a body of water that is behind or within the baffle.
Such buoyant structures, with hanging baffles attached, help to inhibit formation as well as propagation of waves within the mattress. They also impart a relatively firm "feel", since they float immediately below and in contact with the mattress top panel, and so can be felt by a user/occupant. Many users prefer this firm "feel"; however, generally they do not like to feel the buoyant structure itself or the baffle itself, so a layer of fiber is generally or often added on the top of the buoyant structure.
Other systems make use of fibrous mats placed within waterbed mattresses to absorb the energy of water motion caused by occupant movement; this is the subject of my U.S. Pat. No. 4,301,560, and is discussed in more detail in subsection (b), below. In these latter systems energy is absorbed by the fibrous structure of the matting. This approach to reducing wave motion can be used to provide a relatively soft "feel," preferred by some users. This kind of "feel" generally results from using fiber that is not significantly buoyant; my U.S. Pat. No. 4,301,560 is not limited to providing this softer "feel."
Yet other systems combine these two effects. That is, they employ some combination structure that offers both (1) buoyancy to support a hydraulic chamber or other hanging baffle, and (2) the capability of absorbing the flow energy or wave energy of water flowing through the structure. In some cases a polyethylene foam sheet or block one-eighth to one-quarter of an inch thick is laminated into the middle of a fiber matting two to six inches thick, to produce such a combined buoyant and energy-absorbing structure. In other cases the foam is placed only below the fiber.
These systems, however, are rather exceptional, the most prevalent being only buoyant structures. Such "only-buoyant" structures are entirely without fiber--except for the thin layer of fiber that is generally placed atop the buoyant structure to prevent its being felt by the user, as previously mentioned. This layer is typically a half-inch to an inch thick.
These various configurations strongly affect the "feel" of the finished mattress, and as already noted different users typically prefer different configurations. On an objective level, however, the solid polyethylene foam pad that is common to all the configurations has several drawbacks:
(1) It interferes with convection currents and thus with effective thermostatting at the area of contact with the occupant of the bed. PA0 (2) It also acts as a reservoir for tiny air bubbles, releasing them a few at a time over a long period of time--and thus requiring the user to bleed them out of the mattress for a relatively long time. PA0 (3) It also interferes with the access of water to the mattress valve when the bed is drained. PA0 (4) The diminished convection currents can also interfere with proper circulation of water-treatment chemicals within the mattress, thereby increasing the likelihood of bacteria and the like growing in the obstructed areas. The result can be both objectionable odor and degradation of the vinyl. PA0 (1) supports the hydraulic chamber, to provide the antiwave characteristic of the chamber, and PA0 (2) itself is partially exposed to the circulation of water within the waterbed mattress and thereby is situated to slightly dampen such circulation in the manner described in my previously mentioned U.S. Pat. No. 4,301,560.
A hydraulic chamber is a preferably nonwatertight inner compartment which damps undesirable waves by the inertia of enclosed water. Because it is vented, a hydraulic chamber allows relatively slow inward and outward water flow, to accommodate filling--and to accommodate relatively slow shifts of water distribution, thereby helping the waterbed mattress to adjust to the position of a person lying on the bed. The unsealed apertures in the chamber are small enough, however, to cause the chamber to behave essentially as a unit in response to transients caused by relatively abrupt motions of the occupant. It is this latter effect that resists and thereby reduces the undesirable wave motion.
A hydraulic chamber is hung from a buoyant pad or other "float" within the mattress. Typically the pad floats just below the upper panel of the mattress, and the chamber hangs downward toward (but generally not all the way to) the bottom panel of the mattress.
Prior buoyant pads used to support hydraulic chambers have been made of polyethylene. Unfortunately, even closed-cell polyethylene has a tendency to slowly waterlog and eventually sink. A representative of the Dow Chemical Company, which manufactures this material, has explained to me:
"Under long-term submersion conditions, polyethylene foam sheet can be expected to pick up some quantity of water, even though the foam has a closed-cell structure. This is due to the slow migration of individual water molecules into and through the polyethylene cell walls. The buoyant force exerted by the foam would, of course, decrease as more and more water molecules make their way into the foam."
This manufacturer estimated the length of time required for this effect to become significant, under conditions pertinent to waterbeds, as "certainly a number of months and possibly several years," and went on to say "we have no data that would allow us to refine this further." I have heard reports of hydraulic-chamber floats waterlogging and sinking in as short a time as eight months, and even six.
Besides forfeiting its antiwave characteristics, a chamber or other continuous structure which sinks can also obstruct convection at the waterbed heater and thermostat. Depending on the geometry and on the electrical circuitry of these devices, various adverse conditions may result--such as causing the thermostat and heater to cycle on and off frequently, and/or to wear out entirely; and/or causing the heater to stay off continuously or to stay on continuously. In the last-mentioned case, accumulated heat could damage the mattress and liner, possibly even releasing the water from the mattress and causing water damage to the premises in which the mattress is installed.
Some mitigation of the uptake of water by polyethylene foam may be obtained by using relatively high-density foam. High-density foam presents a greater number of cell walls through which water must migrate to occupy the foam. Unfortunately, however, any material with higher density has correspondingly lower buoyancy, and polyethylene foam is no exception. Thus the manufacturer using floats made of polyethylene foam has a choice of providing brief buoyancy or lower buoyancy! The cost, weight and bulk implications of the latter are apparent. Bulk, in particular, is undesirable since it places a lower limit on the overall size of the unfilled waterbed mattress for shipment and storage.
One seductive solution to this problem is to encapsulate the polyethylene foam pad in vinyl--or in some other sheeting similar to that used for the mattress proper. There are at least two drawbacks to this solution.
First, the encapsulation tends to aggravate the tendency of polyethylene pads to obstruct heat flow vertically within the mattress. This obstruction prevents the thermostatted waterbed heater (in conjunction with convective circulation) from controlling the water temperature as felt by the occupant of the bed. To overcome this problem one may manufacture the pad and its encapsulation with multiple apertures--but this substantially increases the number of separate welded seams, and thus the labor and the manufacturing cost.
Second, encapsulation forecloses any possibility of using the structure of the buoyant pad itself for wave absorption; however, since satisfactory buoyant pads of fibrous material have not previously been available, this possibility has not been significant before now.
(b) Fiber products--Polyester fiber has many applications, including use in waterbed mattresses for the purpose of inhibiting wave motion. Developments in this area are set forth in my U.S. Pat. No. 4,301,560, entitled "Waterbed Mattress", which issued Nov. 24, 1981, and is hereby incorporated by reference. As shown in that patent, bonded nonwoven polyester fiber disposed within a waterbed mattress very effectively reduces undesirable wave motion.
One very undesirable form of wave motion occurs near the upper surface of the mattress. This portion of the wave motion can be inhibited by positioning the fiber in the upper part of the mattress, using appropriate means. One way to accomplish this is to fill substantially all of the mattress with the fiber. The fiber, which is nonbuoyant, rests on the bottom, inner surface of the mattress and extends upward into the upper portions of the mattress.
Although wave motion can be effectively reduced in the manner described above, the necessity of filling substantially all of the mattress with the fiber is a serious drawback. The large required amount of fiber increases the shipping size and weight of the mattress and, more importantly, significantly increases the cost of manufacturing the mattress. Handling and storage are likewise adversely affected.
Another way to position fiber in the upper part of the mattress is to render the bonded fiber buoyant in some manner. (The term "buoyant" as used in this document means buoyant in water.) As already mentioned, one prior-art approach is to construct a laminated fiber pad composed of an upper layer of fiber, a middle layer of buoyant foam material, and a lower layer of fiber. The buoyant foam material can be either a thin foam pad or a thin layer of foam beads. The laminated pad is held together by suitable adhesives, stitching, riveting and other similar methods.
Such prior-art buoyant laminated pads are effective in suppressing wave motion. However, such pads are subject to a high rate of failure by delamination, apparently due to the high forces encountered in use. They are also relatively expensive to manufacture because of the large amount of manual labor required in the manufacture.
Another prior-art attempt to produce a buoyant fiber product involves the use of polypropylene fiber. This fiber, unlike polyester fiber, is buoyant in water. Unfortunately, however, if polypropylene fiber is made into a unitary matting by means of a commonly used bonding agent such as acrylic latex, the buoyancy of the fiber is reduced and may be rendered inadequate. Experiments have been conducted with buoyant bonding agents, but it is not believed that any of such experiments have been successful.
The prior art thus has failed to provide a buoyant fiber product (or any other means) that is reliably effective and practical for the reduction of wave motion in waterbed mattresses.